1. Field of the Invention
The present invention relates generally to the art of refrigeration. More particularly, this invention is directed to the modification of a basic heat pump circuit to additionally accomplish the heating of a liquid, such as hot water for domestic applications. With still more particularity, the present invention relates to an air-to-air heat pump circuit capable of heating a liquid and in which heat for defrost of the outdoor coil is capable of being supplied entirely from stored, previously heated liquid. Finally, this invention relates to a heat pump circuit capable of (1) cooling a space; (2) heating a space; (3) heating a liquid without affecting the temperature of a conditioned space; (4) cooling a space while heating a liquid; (5) heating a space while heating a liquid; and, in addition to the standard method of defrost wherein defrost heat is supplied from a conditioned space, is capable of (6) defrosting the outdoor coil using only stored previously heated liquid as a heat source.
2. Background Art
Commonly available devices known as heat pumps are reversible refrigeration systems capable of conditioning a space by heating or cooling the air within the space. Outdoor air is used as a heat source or heat sink depending upon the particular mode of heat pump operation. The use of heat pump systems to additionally provide for the heating of a liquid utilizing heat otherwise rejected as waste heat has previously been recognized as being energy efficient. Representative in this regard are U.S. Pat. Nos. 3,916,638 to Schmidt; 4,299,098 to Derosier and 4,528,822, to Glamm, the latter two being assigned to the assignee of the present invention. The aforementioned hot water heating heat pump systems cannot, however, accomplish the heating of water while the heating of a space is simultaneously occurring. Even more versatile than the aforementioned circuits are the heat pump systems taught by U.S. Pat. Nos. 3,188,829 to Siewert et al, 4,098,092 to Singh and 4,399,664 to Derosier, the last being assigned to the assignee of the present invention. All of these disclose heat pump circuits having the capability to heat water while simultaneously providing heat to a space.
One disadvantage, inherent in the operation of air-to-air heat pump systems, relates to the buildup of frost on the outdoor heat exchanger coil when indoor space heating is called for in the heating season and outdoor ambient conditions are conducive to the buildup of frost on the outdoor coil as heat is extracted from the ambient. When conditions are conducive to frost buildup, moisture is precipitated out of the cool air being drawn over and through the outdoor coil at the coil surface where it solidifies in the form of frost or ice. The buildup of frost insulates the heat exchanger coil with the result that the heat exchange capability of the coil is degraded and the ability of the heat pump circuit to deliver heat to heat water and/or a conditioned space suffers markedly. The need for timely and effective defrost of the outdoor coil naturally follows.
A common method of defrosting the outdoor coil in a heat pump circuit is known as reverse cycle defrost which entails reversing the operation of the heat pump system from the space heating mode to the space cooling mode of operation. The effect of such mode reversal is to direct the hot gas discharged by the compressor within the system directly to the outdoor coil, as normally occurs in the space cooling mode, as opposed to directing the hot gas to the indoor heat exchanger as normally occurs in the space heating mode.
During periods of space heating the indoor coil acts as a condenser and the outdoor coil as an evaporator with the result that heat from the hot refrigerant gas discharged from the compressor is given up to the indoor space while heat is extracted from the outdoor ambient for ultimate use indoors. In current reverse cycle defrost schemes, i.e., when a heat pump is shifted to what would normally be a space cooling mode, heat is given up to the outdoor coil, which functions as a condenser, and melts the frost buildup on the coil. Since the indoor coil functions as an evaporator in reverse cycle defrost modes it extracts heat from its surroundings, i.e., the heated indoor space. The extraction of heat and the resultant lowering of the temperature of the indoor space when conditions in fact call for space heating is clearly an undesirable result and has previously required the energization of a supplemental heat source, such as electrical resistance heaters or a furnace, while the heat pump system is in the defrost mode. The net result of the use of such supplemental heating is the defrost of the outdoor coil at a coefficient of performance of approximately 1.0. See for example the heat pump system illustrated in recently issued U.S. Pat. Nos. 4,493,194 to Bricetti and 4,476,920 to Drucker. Such supplemental heat is significantly more expensive than the heat provided by the heat pump system just as is the electrical resistance heat utilized to heat water in conventional water heating systems. In none of the previously noted art is there disclosed a heat pump system sufficiently versatile to simultaneously heat a space and a liquid in one mode while offering a defrost mode in which the condition of an indoor space is unaffected and in which the source of defrost heat is exclusively a stored previously heated liquid. As should be apparent from the stream of related U.S. patents continuing to issue in this area the need remains for a more versatile and energy efficient heat pump system which is capable of simultaneously heating a space while heating a liquid and which offers defrost of the outdoor heat exchanger coil without the extraction of heat from a heated space.